diff --git a/addons/rose/addon/components/rose/form/radio/group/index.hbs b/addons/rose/addon/components/rose/form/radio/group/index.hbs
index 76cfea93b..fc34bd1cc 100644
--- a/addons/rose/addon/components/rose/form/radio/group/index.hbs
+++ b/addons/rose/addon/components/rose/form/radio/group/index.hbs
@@ -1,3 +1,3 @@
 {{yield (hash
-  radio=(component 'rose/form/radio/radio' name=@name selectedValue=@selectedValue disabled=@disabled)
+  radio=(component 'rose/form/radio/radio' name=@name selectedValue=@selectedValue disabled=@disabled changed=@changed)
 )}}
diff --git a/addons/rose/addon/components/rose/form/radio/group/index.stories.mdx b/addons/rose/addon/components/rose/form/radio/group/index.stories.mdx
index ebdb50560..be2871af1 100644
--- a/addons/rose/addon/components/rose/form/radio/group/index.stories.mdx
+++ b/addons/rose/addon/components/rose/form/radio/group/index.stories.mdx
@@ -1,5 +1,6 @@
 import { Meta, Story, Preview } from '@storybook/addon-docs/blocks';
 import { hbs } from 'ember-cli-htmlbars';
+import { action } from '@storybook/addon-actions';
 import { text, boolean } from '@storybook/addon-knobs';
 
 <Meta title="Rose|Form/Radio/Group" component="Form/Radio/Group" />
@@ -13,6 +14,7 @@ Renders a form radiofield group.
   @disabled={{false}}
   @name={{name}}
   @selectedValue="disagree"
+  @changed={{fn}}
   as |radioGroup|
 >
   <radioGroup.radio
@@ -36,6 +38,7 @@ Renders a form radiofield group.
       @disabled={{disabled}}
       @name={{name}}
       @selectedValue={{selectedValue}}
+      @changed={{changed}}
       as |radioGroup|
     >
       <radioGroup.radio
@@ -62,6 +65,7 @@ Renders a form radiofield group.
     secondFieldValue: text('second value', 'maybe'),
     thirdFieldLabel: text('third label', 'Disagree'),
     thirdFieldValue: text('third value', 'disagree'),
+    changed: action('changed')
   }
   }}</Story>
 </Preview>
diff --git a/addons/rose/addon/components/rose/form/radio/radio/index.hbs b/addons/rose/addon/components/rose/form/radio/radio/index.hbs
index 4e38ecb4f..9b037d7fb 100644
--- a/addons/rose/addon/components/rose/form/radio/radio/index.hbs
+++ b/addons/rose/addon/components/rose/form/radio/radio/index.hbs
@@ -9,7 +9,8 @@
     @name={{@name}}
     @value={{@value}}
     @groupValue={{@selectedValue}}
-    @disabled={{@disabled}}/>
+    @disabled={{@disabled}}
+    @changed={{@changed}} />
 
   <label class="rose-form-radio-label" for={{this.id}}>
     {{@label}}
diff --git a/addons/rose/addon/components/rose/form/radio/radio/index.stories.mdx b/addons/rose/addon/components/rose/form/radio/radio/index.stories.mdx
index 91d256e9a..3aeae1f22 100644
--- a/addons/rose/addon/components/rose/form/radio/radio/index.stories.mdx
+++ b/addons/rose/addon/components/rose/form/radio/radio/index.stories.mdx
@@ -15,6 +15,7 @@ Renders a form radiofield.
   @value="yes-agree"
   @selectedValue="yes-agree"
   @disabled={{false}}
+  @changed={{fn}}
   />
 ```
 
diff --git a/addons/rose/tests/integration/components/rose/form/radio/group-test.js b/addons/rose/tests/integration/components/rose/form/radio/group-test.js
index b8e6f7fc0..dfd2e4bce 100644
--- a/addons/rose/tests/integration/components/rose/form/radio/group-test.js
+++ b/addons/rose/tests/integration/components/rose/form/radio/group-test.js
@@ -52,9 +52,15 @@ module('Integration | Component | rose/form/radio/group', function (hooks) {
     assert.equal(findAll('[type="radio"]')[1].checked, false);
   });
 
-  test('it reflects active radiofield value in @selectedValue', async function (assert) {
+  test('it reflects active radiofield value in @selectedValue and triggers a @changed function', async function (assert) {
+    assert.expect(5);
+    this.changed = (value) => assert.ok(value);
     await render(hbs`
-      <Rose::Form::Radio::Group @name="bird" @selectedValue={{this.selectedValue}} as |radioGroup|>
+      <Rose::Form::Radio::Group
+        @name="bird"
+        @selectedValue={{this.selectedValue}}
+        @changed={{this.changed}}
+      as |radioGroup|>
         <radioGroup.radio
           @name="bird"
           @label="Pegion"
diff --git a/ui/core/app/routes/application.js b/ui/core/app/routes/application.js
index 804c2896e..6d4eee236 100644
--- a/ui/core/app/routes/application.js
+++ b/ui/core/app/routes/application.js
@@ -26,6 +26,11 @@ export default class ApplicationRoute extends Route.extend(
 
   // =methods
 
+  beforeModel() {
+    const theme = this.session.get('data.theme');
+    this.toggleTheme(theme);
+  }
+
   /**
    * After becoming authenticated, does nothing.  This overrides the default
    * behavior of the ApplicationRouteMixin, which is to redirect after auth.
@@ -115,4 +120,29 @@ export default class ApplicationRoute extends Route.extend(
     }
   }
 
+  /**
+   * Applies the specified color theme to the root ember element.
+   * @param {string} theme - "light", "dark", or nullish (system default)
+   */
+  @action
+  toggleTheme(theme) {
+    const rootElementSelector = getOwner(this).rootElement;
+    const rootEl = getOwner(this).lookup('service:-document')
+      .querySelector(rootElementSelector);
+    this.session.set('data.theme', theme);
+    switch (theme) {
+      case 'light':
+        rootEl.classList.add('rose-theme-light');
+        rootEl.classList.remove('rose-theme-dark');
+        break;
+      case 'dark':
+        rootEl.classList.add('rose-theme-dark');
+        rootEl.classList.remove('rose-theme-light');
+        break;
+      default:
+        rootEl.classList.remove('rose-theme-dark');
+        rootEl.classList.remove('rose-theme-light');
+    }
+  }
+
 }
diff --git a/ui/core/app/templates/application.hbs b/ui/core/app/templates/application.hbs
index 50a823972..268d4be15 100644
--- a/ui/core/app/templates/application.hbs
+++ b/ui/core/app/templates/application.hbs
@@ -23,11 +23,33 @@
               {{t 'actions.change-password'}}
             </dropdown.link>
             <dropdown.separator />
+
             <dropdown.button
               {{on "click" (route-action "invalidateSession")}}
             >
               {{t 'actions.deauthenticate'}}
             </dropdown.button>
+
+            <dropdown.separator />
+
+            <Rose::Form as |form|>
+              <form.radioGroup
+                @name="theme"
+                @selectedValue={{this.session.data.theme}}
+                @changed={{route-action "toggleTheme"}}
+              as |radioGroup|>
+                <dropdown.item>
+                  <radioGroup.radio @label={{t "themes.system"}} />
+                </dropdown.item>
+                <dropdown.item>
+                  <radioGroup.radio @label={{t "themes.light"}} @value="light" />
+                </dropdown.item>
+                <dropdown.item>
+                  <radioGroup.radio @label={{t "themes.dark"}} @value="dark" />
+                </dropdown.item>
+              </form.radioGroup>
+            </Rose::Form>
+
           </utilities.dropdown>
         </header.utilities>
 
diff --git a/ui/core/tests/acceptance/authentication-test.js b/ui/core/tests/acceptance/authentication-test.js
index e4965ce8e..9de13e9c8 100644
--- a/ui/core/tests/acceptance/authentication-test.js
+++ b/ui/core/tests/acceptance/authentication-test.js
@@ -6,6 +6,7 @@ import {
   click,
   find,
   findAll,
+  getRootElement
   //setupOnerror,
 } from '@ember/test-helpers';
 import { setupApplicationTest } from 'ember-qunit';
@@ -315,4 +316,29 @@ module('Acceptance | authentication', function (hooks) {
       'Session is unauthenticated, after encountering 401'
     );
   });
+
+  test('color theme is applied from session data', async function (assert) {
+    assert.expect(12);
+    authenticateSession({ scope: { id: globalScope.id, type: globalScope.type } });
+    // system default
+    await visit(orgsURL);
+    assert.notOk(currentSession().get('data.theme'));
+    assert.notOk(getRootElement().classList.contains('rose-theme-light'));
+    assert.notOk(getRootElement().classList.contains('rose-theme-dark'));
+    // toggle light mode
+    await click('[name="theme"][value="light"]');
+    assert.equal(currentSession().get('data.theme'), 'light');
+    assert.ok(getRootElement().classList.contains('rose-theme-light'));
+    assert.notOk(getRootElement().classList.contains('rose-theme-dark'));
+    // toggle dark mode
+    await click('[name="theme"][value="dark"]');
+    assert.equal(currentSession().get('data.theme'), 'dark');
+    assert.notOk(getRootElement().classList.contains('rose-theme-light'));
+    assert.ok(getRootElement().classList.contains('rose-theme-dark'));
+    // toggle system default
+    await click('[name="theme"][value=""]');
+    assert.notOk(currentSession().get('data.theme'));
+    assert.notOk(getRootElement().classList.contains('rose-theme-light'));
+    assert.notOk(getRootElement().classList.contains('rose-theme-dark'));
+  });
 });
diff --git a/ui/core/translations/en-us.yaml b/ui/core/translations/en-us.yaml
index d208e7102..58629f229 100644
--- a/ui/core/translations/en-us.yaml
+++ b/ui/core/translations/en-us.yaml
@@ -25,3 +25,7 @@ questions:
   delete-confirm: Are you sure you want to delete this resource?
   remove-confirm: Are you sure you want to remove this association?
   abandon-confirm: Are you sure you want to navigate away?  Your unsaved changes will be lost.
+themes:
+  system: System Default
+  light: Light
+  dark: Dark